Go back to opening screen 9 Chapter 2 Physical/Geographical Characteristics of the Arctic –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Contents 2.2.1. Climate boundaries 2.1. Introduction . 9 On the basis of temperature, the Arctic is defined as the area 2.2. Definitions of the Arctic region . 9 2.2.1. Climate boundaries . 9 north of the 10°C July isotherm, i.e., north of the region 2.2.2. Vegetation boundaries . 9 which has a mean July temperature of 10°C (Figure 2·1) 2.2.3. Marine boundary . 10 (Linell and Tedrow 1981, Stonehouse 1989, Woo and Gre- 2.2.4. Geographical coverage of the AMAP assessment . 10 gor 1992). This isotherm encloses the Arctic Ocean, Green- 2.3. Climate and meteorology . 10 2.3.1. Climate . 10 land, Svalbard, most of Iceland and the northern coasts and 2.3.2. Atmospheric circulation . 11 islands of Russia, Canada and Alaska (Stonehouse 1989, 2.3.3. Meteorological conditions . 11 European Climate Support Network and National Meteoro- 2.3.3.1. Air temperature . 11 2.3.3.2. Ocean temperature . 12 logical Services 1995). In the Atlantic Ocean west of Nor- 2.3.3.3. Precipitation . 12 way, the heat transport of the North Atlantic Current (Gulf 2.3.3.4. Cloud cover . 13 Stream extension) deflects this isotherm northward so that 2.3.3.5. Fog . 13 2.3.3.6. Wind . 13 only the northernmost parts of Scandinavia are included. 2.4. Physical/geographical description of the terrestrial Arctic 13 Cold water and air from the Arctic Ocean Basin in turn 2.4.1. General geographical description . 13 push the 10°C isotherm southward in the region of North 2.4.2. Geology and physiography . 15 America and northeast Asia, taking in northeastern Labra- 2.4.3. Permafrost and soils . 16 dor, northern Quebec, Hudson Bay, central Kamchatka, and 2.5. Arctic freshwater environments . 17 2.5.1. Rainfall and snow . 17 much of the Bering Sea (Stonehouse 1989). 2.5.2. Groundwater . 17 Another geographical indicator of the Arctic region that is 2.5.3. Wetlands . 17 2.5.3.1. Lowland polygon bogs and fens . 17 partially determined by climate is the presence of permafrost 2.5.3.2. Peat mound bogs . 18 (Barry and Ives 1974). The southern boundary of continu- 2.5.3.3. Snowpatch fens . 18 ous permafrost is shown in Figure 2·11. 2.5.3.4. Tundra pool shallow waters . 18 2.5.3.5. Floodplain marshes . 18 2.5.3.6. Floodplain swamps . 18 2.5.3.7. Wetland occurrence . 18 2.5.4. Rivers . 18 2.5.5. Lakes . 19 2.5.6. Estuaries . 20 2.6. Arctic marine environment. 20 2.6.1. Geographical area and bathymetry . 20 2.6.2. Hydrographic conditions in the Arctic . 21 2.6.3. Ocean currents . 23 2.6.4. Sea ice . 23 Acknowledgments . 23 References . 23 2.1. Introduction The vast region of the Arctic extends across northern North America, northern Europe and northern Asia, taking in eight countries and the expanses of sea and ocean in between. The terrestrial, freshwater and marine environments throughout this area exhibit considerable variation in climate, meteoro- logy and physical geography. This chapter describes this di- versity as a background to discussions on contaminants and AMAP area other stressors in these environments. Arctic marine boundary Arctic circle 2.2. Definitions of the Arctic region 10 C July isotherm Figure 2·1. The Arctic as defined by temperature (after Stonehouse 1989), The Arctic is often delimited by the Arctic Circle (66°32'N) and the Arctic marine boundary, also showing the boundary of the AMAP (Figure 2·1), which approximates the southern boundary of the assessment area. midnight sun. Such a definition, however, is simplistic, given variations in temperature, presence of mountain ranges, distri- 2.2.2. Vegetation boundaries bution of large bodies of water, and differences in permafrost occurrence. Outlined below are some definitions of the Arctic A floristic boundary used to delimit the terrestrial Arctic is region which take into account physical, geographical and/or the treeline (Figure 2·2) (Linell and Tedrow 1981). Simply ecological characteristics. Following these, the Arctic region, as defined, the treeline is the northern limit beyond which trees defined for the purposes of the AMAP assessment, is discussed. do not grow. More accurately, it is a transition zone between 10 AMAP Assessment Report 76°N. Warm Pacific water passing through the Bering Strait meets the Arctic Ocean water at approximately 72°N, from Wrangel Island in the west to Amundsen Gulf in the east (Stonehouse 1989). However, once it passes through the Bering Strait, Pacific water begins to undergo modification on the broad Chukchi shelf due to ice-related processes (freezing, melting, cooling) and the addition of runoff. Modified water becomes incorporated into the surface mixed layer or subducts and flows down the undersea can- yons to contribute to the halocline. Recognizing the diffi- culty of assigning a distinct boundary separating Pacific water from Arctic water, the boundary is arbitrarily drawn across Bering Strait as the point at which modification is likely to commence. Similarly, for the purposes of the AMAP assessment, and recognizing other factors which may be used to define the Arctic marine area, such as Arctic marine biology and sea ice cover, the AMAP marine area to the south of the region as defined above also includes: Davis Strait, the Labrador Sea and Hudson Bay; the Greenland, Iceland, Norwegian, Barents, Kara and White Seas; and the Bering Sea. 2.2.4. Geographical coverage High Arctic Subarctic of the AMAP assessment Low Arctic Treeline Given the different definitions of the Arctic, based on phys- Figure 2·2. Arctic and subarctic floristic boundaries (Bliss 1981, Linell and ical-geographical characteristics as described above, and Tedrow 1981, Nordic Council of Ministers 1996). those based on political and administrative considerations within different countries, no simple delineation of the Arc- continuous boreal forest and tundra, with isolated stands of tic region was applicable for the purposes of the AMAP as- trees. In North America, the tundra-forest boundary is a nar- sessment. To establish a geographical context for the AMAP row band, but in Eurasia this region can be up to 300 km assessment, therefore, a regional extent was defined based wide (Stonehouse 1989). It corresponds with the climatic on a compromise among various definitions. This incorpo- zone where the Arctic air masses meet the air masses orig- rates elements of the Arctic Circle, political boundaries, veg- inating from the south over the subarctic (Bryson 1966 in etation boundaries, permafrost limits, and major oceano- Larsen 1973). graphic features. The region covered by AMAP is, therefore, The treeline roughly coincides with the 10°C July iso- essentially the terrestrial and marine areas north of the Arc- therm (Stonehouse 1989, Woo and Gregor 1992). How- tic Circle (66°32'N), and north of 62°N in Asia and 60°N in ever, in some areas, the treeline lies 100-200 km south of North America, modified to include the marine areas north the isotherm, adding western Alaska and the western Aleu- of the Aleutian chain, Hudson Bay, and parts of the North tians to the Arctic region (Stonehouse 1989). Atlantic Ocean including the Labrador Sea. The Arctic region is often divided by ecologists into the As stated above, the AMAP boundary was established High Arctic and the Low Arctic as shown in Figure 2·2 to provide a geographical context for the assessment, in and described in chapter 4, section 4.4.1. South of the particular source-related assessment issues, i.e., considera- Arctic is the subarctic, the region lying between the closed- tion of sources within and outside the Arctic. The relevance canopy boreal forests to the south and the treeline to the of the AMAP boundary (Figure 2·1) varies when consider- north (Figure 2·2). This region, which combines character- ing different issues, and it has therefore been applied ac- istics of both the boreal forest and the Arctic tundra, is cordingly. Thus, contaminant levels in biota are addressed also referred to as the taiga or forest tundra. The southern in relation to the geographical occurrence of the species boundary of the subarctic generally corresponds with the concerned; demographic data are discussed in relation to southern limits of discontinuous and sporadic permafrost. administrative regions on which, for example, census data Thus, permafrost is present throughout most of the sub- are collected. arctic (Linell and Tedrow 1981). 2.2.3. Marine boundary 2.3. Climate and meteorology 2.3.1. Climate Based on oceanographic characteristics, the marine bound- ary of the Arctic is situated along the convergence of cool, The polar areas are characterized by low air temperatures. less saline surface waters from the Arctic Ocean and warm- This is because they receive, on an annual basis, less solar er, saltier waters from oceans to the south (Figure 2·1). In radiation than other parts of the world. However, the radia- the eastern Canadian Arctic Archipelago, this zone exists tion levels vary greatly depending on the season. In the win- approximately along a latitude of 63°N, and swings north ter months, there is a total lack of incoming solar radiation, between Baffin Island and the west coast of Greenland. Off while in the summer, the poles receive higher levels of solar the east coast of Greenland, the marine boundary lies at ap- radiation than any other place on Earth. proximately 65°N. The warming effect of the North Atlan- The annual amount of solar radiation received is less than tic Current deflects this boundary north of 80°N west of that which is lost to space by long-wave radiation, since a Spitsbergen, while it moves southward in the Barents Sea to large part of the solar radiation that reaches the Earth is re- Chapter 2 · Physical/Geographical Characteristics of the Arctic 11 flected by extensive cloud, snow and ice cover.